RNase H and Multiple RNA Biogenesis Factors Cooperate to Prevent RNA:DNA Hybrids from Generating Genome Instability

SummaryGenome instability, a hallmark of cancer progression, is thought to arise through DNA double strand breaks (DSBs). Studies in yeast and mammalian cells have shown that DSBs and instability can occur through RNA:DNA hybrids generated by defects in RNA elongation and splicing. We report that in yeast hybrids naturally form at many loci in wild-type cells, likely due to transcriptional errors, but are removed by two evolutionarily conserved RNase H enzymes. Mutants defective in transcriptional repression, RNA export and RNA degradation show increased hybrid formation and associated genome instability. One mutant, sin3Δ, changes the genome profile of hybrids, enhancing formation at ribosomal DNA. Hybrids likely induce damage in G1, S and G2/M as assayed by Rad52 foci. In summary, RNA:DNA hybrids are a potent source for changing genome structure. By preventing their formation and accumulation, multiple RNA biogenesis factors and RNase H act as guardians of the genome.

► Defects in many aspects of RNA biogenesis cause RNA:DNA hybrids to accumulate
► Endogenous RNases H are part of a surveillance mechanism that removes RNA:DNA hybrids
► Hybrids form at many loci, both spontaneously and through RNA biogenesis mutants
► RNA:DNA hybrids induce Rad52 foci in G1, S and G2/M of the cell cycle